Many industrial applications require force-actuated mechanical switches. Such mechanical switches provide reliable isolation when in an open state, and provide a low resistance electrical path when in a closed state. However, conventional force-actuated mechanical switches are relatively large and have relatively slow switching speeds. Moreover, conventional force-actuated mechanical switches are typically difficult and costly to fabricate. In addition, it may be difficult to control the sensitivity of force-actuated mechanical switches.
One application of a force-actuated mechanical switch is as a safety switch to avoid accidental deployment of air bags (i.e., air bag switches). In this case, the air bag switch is mounted in an automobile. The air bag switch remains in an open state when the external force applied to the air bag switch is less than a threshold, which is usually, characterized in g's. (A "g" is defined as a force resulting from an acceleration of 9.8 meters/second.sup.2.) When the external force applied to the air bag switch is greater than a predetermined threshold (e.g., when the automobile is in a head on collision) the air bag switch is forced into a closed state, thereby allowing deployment of the air bag.
Force-activated mechanical switches or sensors are also used as shock sensors in computer disk drives. In the case of rigid disk drives, when the mechanical shock or vibration imposed by the environment is excessive, the drive electronics must be able to detect such a disturbance and turn off the read/write circuits in order to avoid overwrite errors. Conventional shock sensors typically use a cantilever beam, which deflects in the presence of external forces. These shock sensors sense the deflection by means of stress imposed on laminated piezopolymeric films or piezoresistive strain gages. Alternatively, these shock sensors can sense the deflection by monitoring the changes in capacitance between the beam and the ground plane.
Similarly, in many other applications, it is desirable to have an analog sensor that outputs a continuous signal proportional to acceleration.
It would therefore be desirable to have a force-activated mechanical switch or sensor which has reliable sensitivity, durability, fatigue and deformation characteristics, has accurate (or linear) operating characteristics, and which can be fabricated at low cost and with batch manufacturing processes.